1. Number of poles of asynchronous motor1. The number of poles of the motorThe number of poles of the motor is the number of magnetic poles of the motor, and the magnetic poles are divided into N poles and S poles, so the number of magnetic poles always appears in pairs. One N pole and one S pole are called a pair of magnetic poles, that is, the number of pole pairs is 1. The electrical angle occupied by a pair of magnetic poles is 360°. In general, the number of stator slots spanned by each group of coils of the motor accounts for a fraction of the total number of slots, and this motor is a few poles.2. The synchronous speed of the motorThe synchronous speed of the motor is the speed n 1 of the rotating magnetic field of the stator , n 1 =60f/P, where n 1 is the synchronous speed in r/min; f is the AC power frequency in Hz; P is the number of pole pairs of the motor.China stipulates that the standard power frequency f=50 Hz , so the rotational speed of the rotating magnetic field is only related to the number of magnetic pole pairs. That is, n 1 =3000/P. It can be seen that the more the number of magnetic pole pairs, the lower the rotational speed of the rotating magnetic field.2-pole motor, number of pole pairs P=1, synchronous speed n 1 =3000 r/min ;4-pole motor, number of pole pairs P=2, synchronous speed n 1 =1500 r/min ;6-pole motor, number of pole pairs P=3, synchronous speed n 1 =1000 r/min ;8-pole motor, number of pole pairs P=4, synchronous speed n 1 =750 r/min ;10-pole motor, number of pole pairs P=5, synchronous speed n 1 =600 r/min .Second, the speed of the asynchronous motorThe rotor speed n of an asynchronous motor cannot be equal to the speed n 1 of the stator's rotating magnetic field , because if n=n 1 , there will be no relative motion between the rotor and the stator's rotating magnetic field, and there will be no induced electromotive force and induced current in the rotor winding, and the rotor cannot be driven to rotate The electromagnetic torque, so there is a difference between the rotor speed n and the stator rotating magnetic field speed n 1 in the operation of the asynchronous motor, and the name "asynchronous" comes from this.1. Slip rate1) There is a speed difference between the speed n of the rotor of the asynchronous motor and the speed n1 of the stator's rotating magnetic field. This speed difference is the speed at which the stator's rotating magnetic field cuts the rotor conductor. Its size determines the size of the rotor electromotive force and its frequency . Direct Affect the working state of the asynchronous motor. The speed difference is represented by slip s: s=(n 1 -n)/n 1 .2) When the rotating magnetic field starts to rotate at the synchronous speed n 1 , the rotor of the motor has not yet rotated due to mechanical inertia, the instantaneous speed of the rotor is n=0, (n 1 -n)=n 1 , and the slip s=1; the rotor turns Afterwards, n>0, (n 1 -n)<n 1 , slip s<1; the rotor rotates with load, there must be enough electromagnetic torque to overcome the resistance torque, and only the rotor speed n is low At the speed n 1 of the stator rotating magnetic field, the relative motion between the rotor and the stator rotating magnetic field can generate a sufficiently large induced electromotive force and induced current to generate a sufficiently large electromagnetic torque. At this time (n 1 -n) > 0, the rotation The difference rate s>0. Therefore, when the asynchronous motor is running normally, 0<s<1. Under rated load operating conditions, s is about 0.01~0.06.2. The speed of the asynchronous motorThe speed formula of the asynchronous motor is n=(1-s)n 1 , that is, n=(1-s)×60f/P, where n is the speed in r/min; f is the AC power frequency in Hz; s is Slip rate; P is the number of pole pairs.From this formula, it can be seen that to change the speed of the asynchronous motor, there are three methods: changing the power frequency f, changing the slip rate s and changing the number of magnetic pole pairs P.
XINDA